The question we are concerned with is the sequence organization of DNA in an animal with very high C-value. At present we have prepared a large number of clones of R1 segments of Necturus DNA and are doing driven reassociation experiments in order to determine the number of homologous sequences present in the chromosomal DNA. We intend to select a segment that is represented more than 50,000 times, which should be easy to do since more than 1/2 of them have this multiplicity. We then intend to find out whether they are dispersed throughout the genome or whether they are clustered into a given region. BIBLIOGRAPHIC REFERENCES: L.A. MacHattie and C.A. Thomas, Jr.: "Viral DNA Molecules," in Handbood of Biochemistry and Molecular Biology, Nucleic Acids 1, 549 (1975). D.C. Gould, H.G. Callan and C.A. Thomas, Jr.: "The Actions of Endonucleases R on Lampbrush Chromosomes." J. Cell Science (1976).